Enhancement of Superconductivity and Structural Instability by Sn Substitution in LaO0.5F0.5BiS2

Layered BiS2-based superconductor La(O,F)BiS2 can exhibit superconductivity via carrier doping, and its super-conducting properties can be changed by applying hydrostatic or chemical pressure through elemental substitution. Single-crystal LaO0.5F0.5BiS2 exhibits filamentary superconductivity with Tc of approximately 3 K. We found that the partial substitution of Bi with Sn in LaO0.5F0.5BiS2 induces a structural phase transition from the P4/nmm to P21/m structure. Bulk superconductivity with Tc of approximately 6 K emerged near this structural phase transition. We also observed filamentary superconductivity with Tc of approximately 8 K, which was approximately three times higher than that of the unsubstituted sample. This finding provides a new route for further increasing the superconducting transition temperature of this system.